Diode and triode devices are widely used in the electronics. One class of these devices utilize the principles of vacuum microelectronics, namely, their operation is based on ballistic movement of electrons in vacuum [Brodie, Keynote address to the first international vacuum microelectronics conference, June 1988, IEEE Trans. Electron Devices, 36, 11 pt. 2 2637, 2641 (1989); I. Brodie, C. A. Spindt, in “Advances in Electronics and Electron Physics”, vol. 83 (1992), p. 1-106]. According to the principles of vacuum microelectronics, electrons are ejected from a cathode electrode by field emission and tunnel through the barrier potential, when a very high electric field (more than 1 V/nm) is locally applied [R. H. Fowler, L. W Nordheim, Proc. Royal Soc. London A119(1928), p. 173].
U.S. Pat. No. 5,834,790 discloses a vacuum microdevice having a field-emission cold cathode. This device includes first electrode and second electrodes. The first electrode has a projection portion with a sharp tip. An insulating film is formed in the region of the first electrode, excluding the sharp tip of the projection portion. The second electrode is formed in a region on the insulating film, excluding the sharp tip of the projection portion. A structural substrate is bonded to the lower surface of the first electrode and has a recess portion in the bonding surface with the lower surface of the first electrode. The recess portion has a size large enough to cover a recess reflecting the sharp tip of the projection portion formed on the lower surface of the first electrode. The interior of the recess portion formed in the structural substrate communicates with the atmosphere outside the device. A support structure is formed on the surface of the second electrode to surround each projection portion formed on the first electrode. With this structure, a vacuum microdevice can be provided which can suppress variations in characteristics due to voids and exhibit excellent long-term reliability.
Triodes (transistors) of another class are semiconductor devices based on the principles of “solid state microelectronics”, where the charge carriers are confined within solids and are impaired by interaction with the lattice [S. M. Sze, Physics of semiconductor devices, Interscience, 2nd edition, New York]. In the devices of this kind, a current is conducted within semiconductors, so the moving velocity of electrons is affected by the crystal lattices or impurities therein. A fundamental drawback of active electronic devices based on semiconductors is that electrons transport is impeded by the semiconductor crystal lattice, which places a limit on both the miniaturization and the switching speed of such devices.
Vacuum microelectronic devices have potential advantages over solid-state microelectronic devices. Vacuum microelectronic devices have a high degree of immunity to hostile environment conditions (such as temperature and radiation) since they are based only on metals and dielectrics. These devices can achieve very high operation frequencies, because the electrons' velocity is not limited by interactions with the lattice [T. Utsumi, IEEE Tans. Electron Devices, 38,10,2276 (1991)]. In general, vacuum microelectronics devices have excellent output circuit (power delivery loop) characteristics: low output conductance, high voltage and high power handling capability. However, their input circuit (control loop) characteristics are relatively poor: they have low current capabilities, low transconductance, high modulation/turn-on voltage and poor noise characteristics. As a result, despite the: tremendous research efforts in this field, these devices found only very few applications, especially as RF signal amplifiers and sources [S. Iannazzo, Solid State Electronics, 36, 3, 301 (1993)].
Most of the current electronics is based on devices which are made from Si or compound semiconductor based structures. Because of the intrinsic resistivity of these devices, the electrons' transmission through the device causes the creation of heat. This heat is the main obstacle in the attempts to maximize the number of transistors within an integrated circuit per a given area.
Semiconductor devices utilizing microtip type vacuum transistors have been developed. Here, electrons move in vacuum and thus, at the highest speed. Therefore, the vacuum transistors can be operated at ultra speeds. However, they suffer from disadvantages in that they are unstable, have relatively short lifetime, and require relatively high voltages for their operation.
U.S. Pat. No. 6,437,360 discloses a MOSFET-like flat or vertical transistor structure presenting a Vacuum Field Transistor (VFT), in which electrons travel a vacuum free space, thereby realizing the high speed operation of the device utilizing this structure. The flat type structure is formed by a source and a drain, made of conductors, which stand at a predetermined distance apart on a thin channel insulator with a vacuum channel therebetween; a gate, made of a conductor, which is formed with a width below the source and the drain, the channel insulator functioning to insulate the gate from the source and the drain; and an insulating body, which serves as a base for propping up the channel insulator and the gate. The vacuum field transistor comprises a low work function material at the contact regions between the source and the vacuum channel and between the drain and the vacuum channel. The vertical type structure comprises a conductive, continuous circumferential source with a void center, formed on a channel insulator; a conductive gate formed below the channel insulator, extending across the source; an insulating body for serving as a base to support the gate and the channel insulator; an insulating walls which stand over the source, forming a closed vacuum channel; and a drain formed over the vacuum channel. In both types, proper bias voltages are applied among the gate, the source and the drain to enable electrons to be field emitted from the source through the vacuum channel to the drain.